1. Field of the Invention
The present invention generally relates to a longitudinal displacement adjustment control arrangement and, more particularly, to a height adjustment control arrangement, particularly for adjusting the height of a chair seat relative to a chair base for office chairs.
2. Description of the Prior Art
Height adjustment columns for adjusting the height of a chair seat relative to a chair base in an office chair are well known. In swivel office chairs having a main screw secured to the bottom of the chair seat and rotatably mounted on the chair base, it has been common practice to provide a nut assembly which can be manually rotated relative to the main screw for adjustment of the seat height. To adjust the seat height, it has been necessary for a user to get off the seat, kneel down below the seat, grasp the nut, and manually rotate the nut on the screw. The nut, or a handwheel associated therewith, can either be rotated about a horizontal or a vertical axis. In either case, many successive twisting motions are necessary to adjust the seat to the proper height. The user typically has to get on and get off the seat several times, and grasp the nut, and repeat the multiple motion rotary action. The manual adjustment of the chair seat of an office swivel chair of this type is disclosed in U.S. Pat. No. 4,087,070.
In further accordance with the prior art, gas-operated cylinder and piston chair control arrangements have been proposed, e.g. see U.S. Pat. No. 4,113,220. Such adjustable gas cylinder controls utilize valves to allow pressurized gas flow between compartments in a cylinder in which a piston is slidably received. Pressure seals are used to contain the pressurized gas in the cylinder. Such pressure seals are subject to frictional wear during adjustment, and tend to fail and leak gas over time. Once the pressurized gas loses pressure and escapes from the cylinder, the adjustable control arrangement is virtually completely useless until a complete overhaul is made, i.e. until the pressure seals are replaced, and the cylinder is recharged with pressurized gas.